For example, stretching before exercise doesn't actually reduce the risk of injury, the American Council on Exercise (ACE) said in a Feb. 14 news release, after examining research conducted over the past decade. However, stretching can help prevent injuries at other times, such as after a workout.

"Static stretching," where you extend a muscle group to its maximum and hold it for up to 30 seconds -- for example, a static leg stretch -- doesn't boost exercise performance, ACE cautioned. On the contrary, static stretching before a workout can have a negative effect on explosive activities, such as sprinting and jumping, and on maximal strength production.

Instead, ACE recommended including some "dynamic" stretches in a warm-up routine. One example of dynamic stretching would be a sprinter doing long, exaggerated strides to prepare for a race, according to the ACE website.

Running is actually better than walking for those who want to burn more calories. Although walking is a great physical activity, the experts stressed, running requires 40 percent more energy.

Finally, lactic acid doesn't really cause acidosis and muscle fatigue during exercise. This myth has commonly been viewed as fact due to the misinterpretation of research. The group said that lactate is helpful during high-intensity exercise.